In numerous rail-transport applications it is standard to secure a running rail to a steel plate that in turn is secured to a concrete sleeper, base, slab or other rigid support surface. The structure must be extremely strong, yet at the same time must have the ability to yield somewhat both vertically and horizontally.
The structure must also permit some limited downward and horizontal movement of the rail plate as the train passes over it. It does not normally need to accommodate upward movement. The downward movement that is permitted, however, must be resisted with a force that prevents the plate from bottoming or over deflecting, yet that still allows some movement to accommodate the passing train.